The present invention relates to rechargeable storage batteries. More specifically, the present invention relates to battery chargers of the type used to charge such batteries.
Chemical batteries which create electricity from chemical reactions have been known for many years. Such batteries are becoming increasing important and have found uses throughout industry. These uses include automobiles, UPS systems, etc.
One advantage of chemical batteries, such as lead acid storage batteries, is that they can be charged and their chemical process reversed by forcing electricity through the battery. Charging systems are widely known in the art and are widely available in the consumer market.
One of the most common techniques for recharging storage batteries is simply placing a voltage source across the battery having a voltage which is greater than the battery voltage. The voltage difference will cause a charging current to flow through the battery causing a reversal of the chemical reaction. The charging current decreases as the voltage difference between the charging voltage and the battery voltage decreases. Typically, the charging voltage is selected to be greater than the nominal battery voltage in order to cause a slight overcharge of the battery. The battery is deemed to be "charged" when the battery will accept no additional current. Frequently, this is through a simple visual inspection of an amp meter on the battery charger by the user of the battery charger. The battery charger may then be switched off.
However, such a simple technique for recharging a battery, although inexpensive, does not provide optimum battery charging and provides very little information about the battery itself. The device does not permit optimal rapid charging of the battery and may lead to excessive overcharging of the battery that can permanently damage the battery and even lead to boiling of the battery electrochemicals causing an unsafe environment. On the other hand, undercharging of a battery results in a battery that is not capable of providing its full potential output. These problems are exacerbated in situations where the battery is rapidly charged using large charging currents.
U.S. Pat. No. 4,956,597, issued Sep. 11, 1990 to Heavey et al. and is assigned to American Monarch Corporation, and entitled "METHOD AND APPARATUS FOR CHARGING BATTERIES" describes one technique in which battery voltage is monitored in an attempt to determine when a battery is fully charged. Another example is shown in U.S. Pat. No. 5,642,031, entitled BATTERY RECHARGING SYSTEM WITH STATE OF CHARGE DETECTION THAT INITIALLY DETECTS WHETHER A BATTERY TO BE CHARGED IS ALREADY AT OR NEAR FULL CHARGE TO PREVENT OVERCHARGING, issued Jun. 24, 1997 to Brotto. The Brotto patent describes a technique in which the charging current is periodically pulsed and the voltage decay is monitored.